The case served as a housing of the battery includes a box and a lid. The box contains an electrode body as a power generating element and has an opening to form a closed-end shape. The plate lid has a shape in accordance with the opening of the box to cover it.
The lid has a pair of through holes from which electric terminals are projected outward. The terminals serve as the positive and negative electrode terminal for transmitting the electric power from the element.
The case is provided with a safety unit such as a relief valve penetrating therethrough in the thickness direction. For example, the relief valve works in the case that the defect such as a short circuit results in generation of large volume of gas, communicating the inside of the battery with the outside to prevent the internal pressure from increasing.
When the battery is a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery, the contamination of water into the battery has an influence on the battery performance, so that the sealing property has to be secured. Furthermore, considering when the inner pressure raises caused by the inside defect, it is worth to seal the other portions to operate the safety unit securely.
Regarding the case of the battery, the box and lid are firmly fixed by welding or the like, so that in the fitted portion of the terminal into the lid, it is required to keep the fitting property of the terminal not to slip out from the lid, the sealing property for preventing from leaking the electrolytes contained in the case and gases generated in the battery, and the insulating property between the terminal and the case.
So, in the battery manufacturing process, especially when fitting the terminal into the through hole formed in the lid, it is important to secure the sealing property of the fitted portion.
Patent Literature 1 discloses a battery having an electric terminal projecting from a lid of the battery, in which an insulating member is arranged between the lid and terminal and the lid is provided with a flanged portion standing out around the insulating member, enabled to keep the sealing property between the lid and the terminal by press-fitting the flanged portion from the direction parallel to the lid, that is the direction perpendicular to the thickness direction of the lid.
Unfortunately, according to the use of the battery, a temperature cycle including heating and cooling is repeated, whereby the press-fitted portion is loosened to return the former shape and the sealing property is degraded.
[Patent Literature 1] JP 2005-302625 A